Tailoring Oxide/MAX Phase Nanocomposites via Low-Temperature Oxidation for Lithium-Ion Battery Anodes: Peeking Behind the Electrochemical Mechanism via In Situ Investigations

This study explores the potential of MAX phase/oxide nanocomposites as negative electrodes for lithium-ion batteries. The main objective is to enhance the stability and performance of tin oxide-based electrodes by reducing volume changes upon cycling. The approach involves the synthesis of a Sn-containing MAX phase (Ti3Al0.3Sn0.7C2) followed by oxidation at different temperatures (600, 700, and 850 °C). Comprehensive characterization reveals that partial oxidation produces nanocomposites containing titanium and tin oxide nanoparticles with different compositions depending on the annealing temperature. The residual presence of the MAX phase contributes to the stability of the electrode, buffering volume changes during cycling. The sample oxidized at 700 °C exhibits the best trade-off between specific capacity (350 mAh g-1 at 50 mA g-1) and reversibility (99.2% Coulombic efficiency), and it delivers a reversible specific capacity of 133 mAh g-1 at 2000 mA g-1 which is superior to the high-rate performance typically reported for graphite. In situ studies provide insights into the mechanism of (de)lithiation, confirming the reduction of Sn(IV) to metallic Sn and the subsequent formation of Li-Sn alloys, while the residual MAX remains electrochemically inactive, preserving structural integrity and transport properties.